Ionization chamber



J. K. EAST ETAM.. ff

INIZATION CHAMBER 4 Filed Jan. 9, 1946 ma Mq.

Patented `an.

UNITED STATES TENT 0 F FICE Energy Commission asentadas January 9, 1946,- seriai No'. 64.11.107 1o claims; (ci. 25o-83.6)

chanical' geometry hasbeen to position in the" path of the alpha emission wire screens diiiering in mesh whereby the proportion of the particles transmitted by the screens may be varied.

The present invention relates to screen type low geometry alpha chambers and has for' an object the provision of such alcha'inbez" in which the geometry is easily and rapidly changeable.

Another object of the invention is topprovide an alpha chamber structure which slinple in construction, permits the ready change of samples andis convenient to clean.

Other objects and advantages of the invention will be readily apparent from the following description when read in connection with theac'- companying drawing in which Fig. l shows in perspective a removable end plate provided with a sample holder and a screen in accordance with the invention;

Fig. 2 is a side elevation in section of a breach type alpha chamber with the end plate of Fig. 1 in position;

Fig. 3 is a fragmentary view in section taken along 3--3 in Fig. 2; and

Figs. 4 and 5 are, respectively, perspective views of interchangeable screen members.

Referring to the drawing and particularly to Fig. 2, there is shown a chamber ID having an upper wall II in which is mounted an insulated collecting electrode I2 and having a removable bottom plate I3 in screw threaded engagement with the chamber IU. A disc I4 of insulating material having integral upstanding opposed side walls I5 is secured to the upper surface of the bottom plate I3 by screws I6 to provide a seat for a U-channeled metal insert consisting of a base plate I'I and side plates I8 having outwardly extended flanges i9 shaped to conform to the side walls I5 of insulating material. This metal insert is secured in position in any suitable manner as by a screw 20 extending through a wall I5 and into a side plate I8.

The side plates I8 of the metal insert are provided with two pairs of longitudinally extending iyways the upper pair cf?- whieh siidabiy sup:

porta keyed plate ZI which lies flush with the flanges- I9 and which has a centrally disposed wire mesh section 22. The lower pair of key-4 vira'ysinv the side plates I8 slidably receive a sam:- ple support block* 23 having an upright post 24j, the topiace of which has a sample'receivingv recess 25. To facilitate the insertion band remoi/'alY of the block' 23 it is provided with avhand` grip 25 which also has` a depending boss 2'I adapted to abut against the front face of the base plate I 'I` of themetal `insert thereby predetermining`- thep'osition of the sample. Thes'creen' carryin'gkeyed plate 2l` is similarly accurately positioned by theprovision thereon of laterally ex` tending ears 28 which abut against the front faces of: the side plates" I8.

The screen carrying keyedA plates of ligsgiy and''are the same as the plate 2i except for the mesh sizein the screen.

From the above' description it will be noted' that the metal insert carryingl the sample supi portblock 23v and the screenplate 2| is insulated from the bottom plate i3 and is thus adapted' to"bec'o`rne the high voltage electrode. For this purpose', one oi the side' platesl I has secured thereto a projectingmetafl a'rin"v 25 positioned to' make wiping engagement with a spring contact 30 extending into the chamber Ill. The contact 3U may be connected to any suitable source of high voltage through a lead 3i passing through the wall of the chamber IQ and electrically isolated therefrom by an insulating block 32. With this arrangement the arm 29 and the contact 30 engage when the bottom plate I3 is screwed into position shown in Fig. 2 and are disengaged when the bottom plate I3 is unscrewed to remove the assembly of Fig. 1 from the chamber IIJ.

As described above, the invention provides a breach type screen low geometry parallel plate alpha chamber in which diierent known geometries may readily be obtained by inserting a proper screen member. The invention also provides a screen member as a part of the removable sample 'holding assembly and as a part of the high voltage electrode.

While for the purpose of illustrating the invention a particular embodiment thereof has been described it is to be understood that many modifications may be made without departing from the invention, the scope of which is pointed out in the appended claims.

We claim:

1. An ionization chamber including a pair of spaced parallel plates adapted to dene an electric field, a sample holder and a removable end plate, characterized by one of said plates being wire mesh and carried by the end plate in overlying relation to the sample holder.

2. In an ionization chamber in combination, means comprising a built in collecting electrode, and a means forming a removable end plate carrying a sample holder and a high voltage electrode, the high voltage electrode including a wire mesh screen overlying the sample holder.

3. In a breach type ionization chamber for alpha counting, a container having a collecting electrode and a removable end plate, said end plate having mounted thereon in spaced relation a perforated high voltage electrode and a and an interchangeable screen member interposed between said first electrode and specimen holder, and Contact members engageable to place said second-mentioned electrode in a circuit when the assembly is in place in the ionization chamber.

8. In anionization chamber, in combination with a first electrode, an electrode assembly comprising a supporting member having a base portion, a perforate member removably mounted in 4 spaced relationship to said base portion, and a sample holder removably mounted between said perforate member and said base portion.

sample holder, said perforate electrode overlying said sample holder.

4. In an alpha chamber the geometry of which I is changed by employing screens of different mesh between an alpha source and the ionization region of the chamber, a removable bottom plate having an electrode assembly mounted thereon, said assembly comprising two spaced parallel Walls having two pairs of vertically spaced horizontally extending keyways, a sample holder removably positioned in the lower pair of keyways, and a screen member removably positioned in the upper pair of keyways.

5. In an ionization chamber, in combination, a rst electrode, a removable assembly forming another electrode comprising a specimen holder and an interchangeable screen member interposed between said rst electrode and specimen holder.

6. In an ionization chamber, in combination, a first electrode, a removable'assembly forming another electrode comprising a specimen holder and an interchangeable screen member interposed between said first electrode and specimen holder, the specimen holder comprising a unit itself removable from the assembly for changing specimens.

7. In an ionization chamber, in combination, a rst electrode, a removable assembly forming another electrode comprising a specimen holder 9. In an ionization chamber, in combination, a first electrode, an electrode assembly comprising a removably mounted member adapted to carry a sample of radioactive material, and a removable perforate member interposed between said radioactive material and said rst electrode. l0.` In an ionization chamber, in combination, a rst electrode, an assembly forming a second electrode and constituting a specimen holder, said assembly being removable from the chamber and being normally spaced from said iirst electrode when the assemblyis in place in the ionization chamber, contact members engageable to place vsaid second electrode in a circuit when said assembly is in place in the ionization chamber, and said assembly having a member removable thereirom which forms the specimen holder.

JACK K. EAST. SPOFFORD G. ENGLISH.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,933,063 Kolhorster Oct. 31, 1933 2,189,874 Ziganke Feb. 13, 1940 FOREIGN PATENTS Number Country Date 252,207 Great Britain Aug. 4, 1927 

